1. Technical Field of the Invention
The present invention relates to technology for processing a voice signal.
2. Description of the Related Art
Technology for converting characteristics of voice has been proposed, for example, by Jean Laroche, “Frequency-Domain Techniques for High-Quality Voice Modification”, Proc. of the 6th Int. Conference on Digital Audio Effects. 2003. This reference discloses technology for converting a fundamental frequency (pitch) and characteristics of voice by appropriately shifting each band component obtained by dividing a spectrum of a voice signal into harmonic components (fundamental harmonic component and higher order harmonic components) in the frequency domain.
However, since the technology of the above noted reference converts a fundamental frequency by shifting band components of the spectrum of a voice signal in the frequency domain, when a harmonic component and another sound component (referred to as “ambient component” hereinafter) are present in each band component, it is difficult to generate a natural voice having a frequency-phase relationship appropriately maintained for both the harmonic component and the ambient component. It is possible to generate a natural voice by respectively adjusting phases of the harmonic component and the ambient component through different methods. However, in case of peculiar voice, for example, a thick voice (thick gravelly voice) or hoarseness (husky voice), an ambient component tends to vary greatly with time, and thus it is difficult to adjust the phase of the ambient component to an appropriate value separately from a harmonic component.